Automatic media thickness compensator for a printer

ABSTRACT

A carriage having a print head thereon is traversed along a platen to enable the print head to print along a line of printing in a serial-type printer. The print head moves with the carriage and is also mounted thereon for independent movement towards and away from the platen. A leaf spring biases the print head towards the platen, and a sensing finger, secured to the print head, contacts and glides along a thin, self-supportable, flexible tape which overlies media of various thickness mounted on the platen to maintain the print head (like a wire matrix) a predetermined distance from the media enabling the print head to print on various thicknesses of media automatically.

United States Patent 11 1 Liles 1 Aug. 7, 1973 1 AUTOMATIC MEDIATHICKNESS 1,874,0I3 8/1932 Kaddeland 11mm 3,627,096 l2/l97l Finnegan 1.'l97/l R COMPENSATOR FOR A PRINTER Inventor: George N. Liks, Dayton,Ohio Primary Examiner koben Pun-my [73] Assignee: The National CashRegister s istant E qginerR. T. Raqler 7 Company, Dayton, OhioAttorney-J. T. Cavender and Albert L. Sessler, Jr.

[22] F1led: Aug. 4, 1972 [57] ABSTRACT PP N-1278i174 A carriage having aprint head thereon is traversed along a platen to enable the print headto print along 52 us. c1. 197/1 R, 340/259, 346/139 c a line of Printingin serial-type w The print head 51 1m.c1 B41] 3/50 moves with thecarriage and is also mounted thereon 581 Field of Search 197/1, 18,49,55, for independent movement towards and y from the 197/126, 128, 137,149; 346/76 R, 74 CH, 74 platen. A leaf spring biases the print headtowards the E, 7 M, 74 MC 39 C, 3 235/619; platen, and a sensing finger,secured to the print head,

, 101/35, 4144; 340/259 contacts and glides along a thin,self-supportable, flexible tape which overlies media of variousthickness 5 Ref C t mounted on the platen to maintain the'print head(like UNTED STATES PATENTS a wire matrix) a predetermined distance fromthe 3 705 408 ""972 K t I 346/139 C media enabling the print head toprint on various thickrone 6 a r 3,146,058 8/1964 Henshaw 346/139 0 ofaummat'cany' 2,141,975 I2/1 938 Finch..,..'. 346/139 A 4 Claims, 8Drawing Figures 26 -36 "W l 1 l E g I V 3 1, f1"? 1 .1 I i l 20 68 l 9O/28 '1 i 66 r I I I 106' 1 l I J i l I l l =Ei:.!.] .i|. -\;llJ| I09 '1'',ir" Q I I 1 I I I -1 L LL1Q9," as

z I) D I I 64 86 l 1 1 I v 1 r 24 1 I 48 l l l 1 l 1 1 5 1 1 i A i 1 21; 3 ti 1 X i 34 H 40 60 1 p T 1 PAIENIEU Au; 7 m5 SHEEI 1 (If 4 sum Q0F 4 FIG. 8

FIG. 6

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a plan view of a portionof a serial-type wire matrix line printer on which the forms compensatorof this invention is mounted. The forms compensator comprises a carriagemeans having a conventional wire matrix print head means 22 mountedthereon. A traversing means 24 traverses the carriage means 20 along aplaten 26 of the printer to enable the print head means to print along aline of printingon the platen. The forms compensator also includes amounting means 28 for mounting the print head means 22 on the carriagemeans 20 to enable the print head means to be reciprocated along a linewhich is perpendicular to the line of printing along the platen. Abiasing means 30 (FIG. 2) is used to resiliently urge the print headmeans 22 towards the platen 26. A sensing means 32,.cooperating with theprint head means 22 is used to sense the thicknesses of the medialocated on the platen and to move the print head means away from saidmedia against the bias of said biasing means 30, as a thicker medium isencountered along the line of printing. The biasing means 30 then movesthe print head means 22 towards the platen 26 as a thinner medium isencountered. This action permits the print head means 22 to be spaced apredetermined distance from the media along the line of printingregardless of the thickness of the particular medium mounted on theplaten and being printed upon.

Media of various thicknesses are shown on the platen 26 in FIG. 1, asfor example, medium 34 may be a single sheet tally or audit roll, andmedium 36 may be a multi-sheet pass or bank book. The forms compensatorof this invention is capable of automatically adjusting the print headmeans 22 relative to the platen 26 in response the thickness of theparticular medium being printed upon. Having media of differentthicknesses mounted on the same platen to be printed upon along a singleline of printing is common in accounting machine practices.

The carriage means 20, alluded to earlier, includes a base 38 havingbrackets 40 upstanding therefrom as shown in FIG. 2. These brackets 40support a horizontally positioned rail 42 which is positioned parallelto the rotating axis of the platen 26, and a flat horizontallypositioned rail 44 is secured to the underside of the rail 42 as shownin FIG. 2. A carriage member 46, of the carriage means 20, abuts againstthe rail 42 and rests upon the rail 44.

A conventional traversing screw 48, of the traversing means 24, passesthrough the carriage number 46, and is coupled thereto by theconstruction shown principally in FIG. 3. This construction includes twonuts and 52 which are inserted into split bushings or protrusions S6 and58 respectively, which bushings are secured to the carriage member 46.The nuts 50 and 52 are adjusted on the traversing screw 48 in aconventional manner so as to provide a minimum of backlash of thecarriage member 46 on the screw 48 over the entire length thereof, andeach nut is then clamped in its associated bushing by a fastener 58 asshown in FIG. 2. The ends of the traversing screw 48 are conventionallysupported in bearings (not shown), and the screw 48 is rotated by aconventional constant-speed motor (synchronous or servo controlled) or astepping motor 60 (FIG. 1) to traverse the carriage means 20 along theplaten 26 as the characters are printed by the wirematrix, print headmeans 22. During printing, the stepping motor 60 runs as a continuousmotor, and the dots printed by the seven print head wires which are ar-'ranged in a column (as described earlier in the Background of theInvention) are really printed on the fly" as the print head means 22 istraversed along the line of printing by the motor 60. The main advantageof the stepping motor 60 is that it is low cost and'fairly easy tocontrol by electronics. Because these aspects may be conventional, theyare not described in detail.

The mounting means 28, for mounting the wire print head means 22 on thecarriage means 20 for reciprocating movement towards and away from theplaten 26, is shown in FIGS. 1, 2, and 3. The mounting means 28 includesa base 62 (best seen in FIG. 3) which base has vertically extendingsides against which plates 64 and 66 are secured by fasteners 68. Theplate 64 has a horizontally positioned V-shaped groove on theouter facethereof, into which groove, a plurality of ball bearings 72-ispositioned. A plate 74, also has a horizontally V- shaped groove thereinwhich groove is complementary in shape to the groove in plate 64, andthe plate 74 is fastenedto the carriage member46 by fasteners 76toretain the ball bearings in the grooves'and support the left end (asviewed in FIG. 3) of the base 62. Apin 78 (FIG. 2) projects from theplate 64 into the associhead'means 22 is mounted on the carriage means20 for perpendicular movement towards and away from the platen 26 whilethe carriage means 20 is being traversed along a print'line on theplaten 26.

The-wire matrix print head means 22 includes a wire matrix print headunit 86 which is secured to the base 62 on the carriage member 46 by twofasteners 88 shown in FIG. 1. The print head unit 86 has conventionalactuators like 90 and print wires or wire plungers 92 which aresupported in a wire guide'or'housing 94, which is supportedon a bracket96 secured to the base 62. The wire plungers92, when actuated, come outof the end 98 (FIG. 1) of the housing 94 and impact against a medium onthe platen. The print head unit 86 is of a known variety which utilizesseven wire plungers 92 located in a vertical line as shown in FIG. 8. Inorder to print a completecharacter, like the letter M,.for example, whenusing a five by seven matrix format, the stepping motor 60-would run asa continuous motor to move the print head along the line of printing onthe platen, and five successive impacts by the print head unit 86 wouldbe required to complete the letter. One prior art print head unit, likethe one described, has control electronics which include a run emitter"clock which is operatively associated with the traversing screw 48 andthe motor 60 to allow the screw to rotate at a constant speed. A printemitterclock also associated with the traversing screw 48 and the motor60 in combination with the control electronics creates the necessaryfire pulses (to the actuators 90) which pulses are phased with themotion of the traversing screw 48 to enable accurate horizontal spacingof the dots produced by the successive impacts of the print head unit86. Because the techniques for energizing the print head unit 86 areconventional, they are not described in detail herein. A plate 100 (FIG.2), secured to the bracket 96, supports two spaced and verticallypositioned posts 102 and 104 which are used as ribbon guides. As shownin FIG. 1, an inked ribbon 106 passes behind post 102, around the frontend of an adjustably fixed deflector guide 107 and one side of the end98 of the housing 94, around the front end 98 of housing 94, around thefront end of an adjustably fixed deflector guide 109 located on theopposite side of the housing 94, and behind the second post 104. Thebracket 96 has a well 108 (FIG. 2) located therein beneath the housing94, and a curved wall 110 and a vertically positioned flat wall 1 12form opposed contact areas in said well.

The biasing means 30 alluded to earlier is shown in FIG. 2. As statedearlier, the biasing means 30 is used to resiliently urge the wirematrix print head means 22 towards the platen 26 along a line which isperpendicular to a line of printing thereon; it should be recalled thatthe print head means 22 is also mounted for reciprocal movement relativeto the platen. The biasing means 30 includes a leaf-type spring 114,having one end fixed to a lever 116 by fasteners 118. The free end ofthe spring 114 passes through a suitable slot in the carriage member 46and extends into the well 108 and abuts against the curved wall 110therein to resiliently urge the print head means 22 towards the platen26 with a force of one-fourth to onehalf pound. The lever l 16 has asquare hole therein between the ends thereof, enabling the lever to beslidably mounted on a bar 120 which is square in cross section asshown-in FIG. 2. The bar 120 extends along the length of the platen andis parallel to the traversing screw 48. Bar 120'has its endconventionally, rotatably mounted in the side frames (not shown) of aprinter in which this invention is located. One end 122 of lever 116passes through a suitable slot in the carriage member 46 and extendsinto the well 108 located in the bracket 96. The remaining end of thelever 116 has two notches 124 and 126 therein to receive apawl member128. The lever 116 also has a hub portion 130 fixed thereto on each sidethereof, and each. hub portion has a square opening therein which isaligned with the square opening in the lever 116 to provide a slidingfit on the square bar 120. Each hub portion like 130 is rotatablymounted in an apertured flange 132 which is secured to the carriagemember 46 by fasteners 134. By this construction, the lever 1.16 iscarried by the carriage member 46 as it is traversed along the platen 26and is capable of being independently rotated in clockwise andcounterclockwise directions by the square bar 120. A lever 136 (FIG. 1)is fixed to the bar 120 by a flange 138 to rotate the bar. One end ofthe lever 136 has an actuating arm 140 of a solenoid 142 securedthereto.

The print head means 22 is moved away from the platen 26 to permit theinsertion of media 34, 36 by the construction just described. When thesolenoid 142 is energized, the operating arm 140 (FIG. 1) rotates thelever 136 and bar 120 in a clockwise direction (as viewed in FIG. 2).When so rotating, the lever 116 which is slidably secured to square bar120, will also be rotated in a clockwise direction enabling end 122thereof to contact the vertical wall 112 in well 108 and move the entireprint head means 22 away from the platen 26 to the position shown by thedashed outline 144 in FIG. 2. The mounting means 28, already described,enable the lever 136 to move the print head means away from the platen26, and it is held in the away position by the pawl member 128 enteringnotch 126 (FIG. 2) after the lever 116 is rotated. When the solenoid 142is deenergized, a spring (not shown) asso' ciated with the operatingplunger thereof, will return the print head means 22 to the positionshown in solid lines in FIG. 2 in which pawl member 128 enters notch 124as shown. This position enables the print head means 22 to move freelytowards the platen 26 to engage it without the end 122 of lever 116contacting the vertical wall 112. The leaf spring 114, secured to lever116, urges the print head means 22 towards the platen 26.

The sensing means 32, (FIGS. 1 and 2) alluded to earlier, cooperateswith the print head means 22 to contact the media on the platen 26 andto move the print head means away from the media as a thicker medium isencountered along the line of printing and to enable the biasing means30 to move the print head means 22 towards the platen as a thinnermedium is encountered, thereby enabling the print head means 22 to bespaced a predetermined distance away from the particular medium beingprinted upon regardless of its thickness. This adjustment is madeautomaticaly without any adjustment by an operator using thisinvention.

The sensing means 32 (FIG. 2) includes a flexible tape means 200,mounting means 202 for mounting the tape means 200, and a sensing finger204.

The mounting means 202 is best shown in FIGS..2 and 6 andincludes ashaft 206 which is secured to the side frames (not shown) of the printerin which this invention is used. A plurality of U-shaped brackets, like208, are rotatably mounted on the shaft 206, and these brackets arespaced equally along the length of the platen 26. Each bracket 208 hasaligned apertures therein to receive a shaft 210 which also extendsalong the length of the platen 26. Shafts 206 and 210 are parallel tothe rotating axis of platen 26. Two rollers 212 and 214 areconventionally, rotatably mounted on the shaft 210 and are locatedbetween the arms of each bracket 208 as shown in FIG. 6. Each bracket208 is fixed at various spaced locations along the length of the platen26 by nuts 216 and 218 which are fastened to threaded portions of theshaft 210. A tension-type spring 220 (FIG. 2) having one end secured tothe arm of the bracket 208 closest to the sideframe (not shown) of theprinter, and the other end of thespring secured to the side frame, isused to resiliently rotate all the brackets 208 and shaft 210 in acounterclockwise direction (as viewed in FIG. 2) to enable the rollerslike 212 and 214 to press the media into contact with the platen, as isconventionally done. The shaft 210 and brackets 208 also support theflexible tape means 200 in the position shown in FIG. 2.

The flexible tape means 200 has the general shape shown principally inFIGS. 4 and 6, and includes an elongated area or tape 220 which extendsalong the length of the platen 26 and has long fingers 222 and shortfingers 224 depending therefrom. The tape means 200 is typically made ofstainless steel, having a thickness of about 0.005 inch, and is flexibleand self supporting. The long fingers 222 and short fingers 224 arespaced apart equal distances, and each adjacent pair of long fingers 222has one of the brackets 208, positioned therebetween as shown in FIG. 6.Each long finger 222' has a curved section 226 on the free end thereofwhich substantially encircles the shaft 210 when positioned thereon asshown in FIG. 6. The shaft 210 has suitable circumferential groovestherein to receive C-type lock rings 228 which restrain each long finger222 from axial movement on the shaft. By this construction, the tapemeans 200 is free to rotate on shaft 210 but is axially restrainedthereon. When the tape means 200 is positioned next to the platen 26,there is a tendency for the tape means to rotate in a clockwisedirection (as viewed in FIG. 2) under the influence of gravity. Thisclockwise rotation occurs when the print head means 22 is moved awayfrom the platen 26 to the position shown by the dashed line 144. To keepthe tape means 200 from rotating away from the platen, a lip 230 isformed on each bracket 208 as shown in FIGS. 2 and 6, and the associatedshort finger 224 of the tape means 200 is then positioned between thelip 230 of the associated bracket 208 and the platen 26.

The sensing finger 204 has a spherically shaped end which contacts andglides along the elongated area or tape 220 of the tape means 200. Thefinger 204 has an axis which is positioned along a radial line from theaxis of the platen 26, and the finger is held in that position by abracket 232 which is secured to the plate 100.

The operation of the sensing means 32 is as follows. Assume that themedium 34 on the platen 26 is a single journal sheet, and that a passbook 36 is positioned over a portion of the sheet 34 as shown in FIGS. 1and 7. The sensing finger 204, tape means 200, and print head means 22are urged against the journal sheet 34 by the leaf spring 114 of thebiasing means 30 (FIG. 2). As the print head means 22 is traversedacross the platen 26 by the traversing means 24, the sensing finger 204glides along the length of the elongated area or tape 220 of the tapemeans 200, pressing against the journal sheet 34 to maintain the end 98of the print head a fixed distance away from the journal sheet 34.Notice that at the junction 232 between the thinner sheet 34 and thethicker pass book 36 (FIG. 7), the tape means 200 provides a gradualtransition therebetween due to the tape means being flexible. As thesensing finger 204 rides over the junction 232, it will push the end 98of the print head away slightly from the platen against the bias of theleaf spring 114 to maintain the end 98 at substantially a fixed distancefrom the pass book 36. As the'print head means 22 is traversed furtherto the right side of the platen 26 (as viewed in FIG. 7), the sensingfinger 204 rides over a junction point 234 between the pass book 36andthe platen 26. At the junction point 234, the tape means 200 provides agradual transition between the pass book 36 and the platen 26 enablingthe biasing means 30 (FIG. 2) to urge the print head means 22 towards Vthe platen 26; the sensing means 32 would then keep the print head means22 a predetermined distance away from the platen 26. Naturally, thispredetermined distance is dependent upon the type of printer used;however in the embodiment shown, this distance was 0.010 inch to 0.025inch.

Upon completion of a line of printing, the platen 26 will be indexed byconventional means, and the print head means 22 will be returned to theleft margin of the ally rotated to rotate square bar in a clockwisedirection (as viewed in FIG. 2), or the solenoid 142 (FIG. 1) may beenergized causing lever 116 to rotate in a clockwise direction andthereby push the print head means 22 away from the platen 26 to theposition shown by the dashed line 144 in FIG. 2. With the print headmeans 22 moved away from the platen, media positioned thereon can beeasily removed and new media can be easily positioned thereon. Thecontrols for operating the stepping motor 60, solenoid 142, platen 26and print head means 22 may be conventional, and accordingly, need notbe described in any further detail. While this invention is described inconjunction with a wire matrix printer, this invention may be used withother printers in which it is desirable to keep the print heads thereofat fixed distances away from media of various thicknesses located on theassociated platens.

FIG. 8 shows the end 98 of the housing 94 as seen from the platen 26.The end 98 has openings 178 therein from which the wire plungers (like92 in FIG. 2) emerge to impact against the media. The housing 94 ismounted on the print head means 22 by the fasteners 186, I88 and 190shown in FIG. 1. The wire plungers (like 92 in FIG. 2) are withdrawnwithin the holes 178 (FIG. 8) when in the inactive state to enable theplungers to be accelerated (when energized) to obtain the requiredhammer impact energy prior to impacting or printing after emerging fromthe holes 178.

When the print head means 22 is traversed at a rapid stepping rate alongthe platen 26 by the traversing means 24, the action of the sensingmeans 32 in riding up a thicker medium on the platen causes a forcepulse urging or bouncing the print head means 22 away from the platen.The faster the stepping or printing rate, the greater is the force pulsewhich is created in moving the print head means 24, and as a result,damping may be needed to minimize the bouncing or moving away of theprint head means from the platen.

A damping means which may be used with this invention, should bouncingof the print head means 22 become a problem, is shown in FIGS. 2 and 3.An elastomeric block 180, made of a material like polyurethane rubber,is bonded to the surface 182 of the base 62 of the print head unit 86and is also bonded to a plate 184 which is free to slide on surface 186of the carriage member 46. The block is compressed sufficiently throughconventinal trial and error techniques so that the combined drag forcecreated by the partially compressed block and plate 184 is a fraction(like onethird to one-half of the force of leaf spring 114 which urgesthe print head unit 86 towards the platen 26. Small motions of the printhead means 22 away from the platen 26 are damped by the block 180 alone,and larger motions of the print head means are additionally clamped bythe sliding of plate 184 on surface 186. If the retract motion of theprint head means 22 to the position shown by the dashed outline 144 isnot desired, the plate 184 can be eliminated, and the block 180 may bebonded directly to the surface 186.

What is claimed is:

1. In a forms compensator for sensing the thicknesses of various mediamounted on a platen of a serial-type line printer having:

a carriage means having-a print head means thereon;

traversing means for traversing said carriage means along said platen toenable said print head means to print along a line of printing on saidplaten;

mounting means for mounting said print head means on said carriage meansfor simultaneous movement therewith along said print line and forindependent reciprocal movement of said print head means along a secondline which is transverse to said line of printing; and biasing means forresiliently urging said print head means along said second line towardssaid platen; the improvement comprising; sensing means secured to saidprint head means to contact the media on said platen and to move saidprint head means away from said media as a thicker medium is encounteredalong said line of printing and to enable said biasing means to movesaid print head means towards said platen as a thinner medium isencountered, thereby enabling said print head means to be spaced apredetermined distance from said media along said line of printingregard: less of the thickness of a particular medium being printed uponon said platen; said sensing means comprising:

a support means extending along the length of said platen; a thin,self-supportable, flexible tape means mounted on said support means andextending along the length of said platen to overlie themedia thereon;

and a finger means fixed to said print head means for contacting saidtape means as said print head means is traversed along said platen.

2. The compensator as claimed in claim 1 in which said tape means has anelongated area'which is positioned parallel to said platen to overliethe media thereon, and said finger means includes a sensing finger whichcontacts said elongated area.

3. The compensator as claimed in claim 2 in which said support meansinclude:

a stationary shaft having its longitudinal axis mounted parallel to saidplaten;

bracket means pivotally mounted on said stationary shaft;

a second shaft mounted parallel to said stationary shaft on said bracketmeans, and spring means to urge said second shaft towards said platen;and

roller means mounted on said second shaft to press the media againstsaid platen;

said tape means further having spaced long fingers depending from saidelongated area, with the free ends of said fingers encircling saidsecond shaft to support said elongated area along said platen.

4. The compensator as claimed in claim 3 in which bracket means havinglip means thereon; and said tape means further having spaced shortfingers depending from said elongated area, with the free endsof saidshort fingers being positioned between said lip means and said platen soas to retain said elongated area near said platen.

I ll i i

1. In a forms compensator for sensing the thicknesses of various mediamounted on a platen of a serial-type line printer having: a carriagemeans having a print head means thereon; traversing means for traversingsaid carriage means along said platen to enable said print head means toprint along a line of printing on said platen; mounting means formounting said print head means on said carriage means for simultaneousmovement therewith along said print line and for independent reciprocalmovement of said print head means along a second line which istransverse to said line of printing; and biasing means for resilientlyurging said print head means along said second line towards said platen;the improvement comprising; sensing means secured to said print headmeans to contact the media on said platen and to move said print headmeans away from said media as a thicker medium is encountered along saidline of printing and to enable said biasing means to move said printhead means towards said platen as a thinner medium is encountered,thereby enabling said print head means to be spaced a predetermineddistance from said media along said line of printing regardless of thethickness of a particular medium being printed upon on said platen; saidsensing means comprising: a support means extending along the length ofsaid platen; a thin, self-supportable, flexible tape means mounted onsaid support means and extending along the length of said platen tooverlie the media thereon; and a finger means fixed to said print headmeans for contacting said tape means as said print head means istraversed along said platen.
 2. The compensator as claimed in claim 1 inwhich said tape means has an elongated area which is positioned parallelto said platen to overlie the media thereon, and said finger meansincludes a sensing finger which contacts said elongated area.
 3. Thecompensator as claimed in claim 2 in which said support means include: astationary shaft having its longitudinal axis mounted parallel to saidplaten; bracket means pivotally mounted on said stationary shaft; asecond shaft mounted parallel to said stationary shaft on said bracketmeans, and spring means to urge said second shaft towards said platen;and roller means mounted on said second shaft to press the media againstsaid platen; said tape means further having spaced long fingersdepending from said elongated area, with the free ends of said fingersencircling said second shaft to support said elongated area along saidplaten.
 4. The compensator as claimed in claim 3 in which bracket meanshaving lip means thereon; and said tape means further having spacedshort fingers depending from said elongated area, with the free ends ofsaid short fingers being positioned between said lip means and saidplaten so as to retain said elongated area near said platen.